Capacitance and dissipation factor measuring apparatus having coherent detectors

ABSTRACT

A dielectric meter for measuring electrical characteristics of a dielectric sample having resistive and capacitive components in which a variable-frequency oscillator has a sine wave output coupled through an integrator with a 1-watt transfer characteristic into a sample; the output of the sample being coupled through an operational amplifier to the input of a first coherent detector and through a limiter to the input of a second coherent detector; the first coherent detector having a reference input comprising an inphase square wave signal from the variablefrequency oscillator and the second coherent detector having a reference input comprising a quadrature square wave signal output coupled from the variable-frequency oscillator; the output of the first coherent detector having an amplitude directly proportional to the capacitor component of the sample and the output of the second coherent detector being passed through a tangent function generator yielding a loss tangent dissipation factor.

Unite States Patent [72] lnventors Stanley A. Yalol PrimaryExaminerEdward E. Kubasiewicz Rte. 1, Box 720, Escondido, Calll. 92025;,4 Ri h -d K. M N ill Lawrence Van Doren, 5119 Arlene Place, San Diego,Calif. 921 17 [2|] APPL N0- 858,266 ABSTRACT: A dielectric meter formeasuring electrical [22] Filed S 16,1969 characteristics of adielectric sample having resistive and [45] Patented Dec. 21, 1971capacitive components in which a variable-frequency oscillator has asine wave output coupled through an integrator with a l-watt transfercharacteristic into a sample; the output of the CAPACITANCE ANDDISSIPATION FACTOR sample being coupled through an operational amplifierto the MEASURING APPARAT HAVING COHERENT input of a first coherentdetector and through a limiter to the DETECTORS input of a second.coherent detector; the first coherent detec- 5 Claims, 1 Drawing 8- tothaving a reference input comprising an inphase square [52] US. Cl 324/60R Wave Signal fmm the Variable-frequency Oscillator and the [51 1 Int Cl1.- 11 52 second coherent detector having a reference input comprising501 Field of Search 324/60 quadrature Square Wave Signal u p coupledfrom the variable-frequency oscillator; the output of the first coherentde- [56] References Cited tector having an amplitude directlyproportional to the capaci- UNITED STATES PATENTS tor component of thesample and the output of the second 3 026 474 3/962 Pi 324/60 coherentdetector being passed through a tangent function generator yielding aloss tangent dissipation factor.

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INVENTOR. STANLEY A. YALOF BY LAWRENCE VAN DOREN CAPACITANCE ANDDISSIPATION FACTOR MEASURING APPARATUS HAVING COHERENT DETECTORS BRIEFDESCRIPTION OF THE INVENTION The present invention relates to adielectric meter and more particularly to a dielectric meter yielding asignal proportional to the capacity of a sample dielectric and a secondoutput yielding a signal proportional to a loss tangent dissipationfactor.

According to the invention, a variable-frequency oscillator has a sinewave output coupled through an integrator yielding a 90 phase shift anda l-watt transfer characteristic. The output of the integrator iscoupled to an input of a sample dielectric material, such as a polyesterresin. The variable-frequency oscillator is set for an optimum frequencyaccording to the impedance characteristics of the particular samplebeing tested. An output is taken from the sample dielectric through anoperational amplifier which will be complex in nature, i.e., the resultof reactive and resistive components in the sample and is coupledthrough a coherent detector which has a reference from thevariable-frequency oscillator to yield a signal having an amplitudevarying directly with capacity component of the sample. This is possibledue to the fact that the reactance of the sample will vary inverselywith frequency while the integrator transfer characteristic has anattenuation varying inversely with frequency which directly compensateeach other for variations in frequency. A second output is taken fromthe operational amplifier through a limiter and a second coherentdetector which has a quadrature reference from the variablefrequencyoscillator which would, without the limiter, yield an outputcorresponding to the phase shift of the signal through the sample.However, by limiting or squaring the input to the second coherentdetector, its output will have an amplitude corresponding to the phaseshift of the signal through the sample. The quadrature reference isnecessary due to the quadrature shift through the integrator resultingin an inphase signal. The output of the second coherent detector ispassed through a tangent function generator which yields a signalproportional to the loss tangent dissipation factor. The termdielectrometer as utilized in this application is defined as aninstrument which meters electrical parameters of a sample dielectricmaterial.

An object of the present invention is the provision of a dielectrometerwhich meters the loss tangent dissipation factor and capacity of asample dielectric material.

Another object is the provision of a dielectrometer in which a signalfrequency can be varied for the optimum transfer characteristics of thedielectric being metered without effecting the output readings.

A further object of the invention is the provision of a dielectrometerwhich utilizes standard components and requires a minimum of maintenanceand adjustment.

Other objects and many of the attendant advantages of this inventionwill be readily appreciates as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings in which like referencenumerals designate like parts throughout the FIGS. thereof and wherein:

The sole FIGURE represents in block diagram form the preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWING Referring to the drawing,variable-frequency oscillator 11 has a set frequency input 12 and oneoutput coupled to integrator 13, a second output connected to areference input of coherent detector 14, a third output connected to areference input of coherent detector 16. The output of integrator 13 iscoupled through sample 17 to the input of operational amplifier 18. Theoutput of operational amplifier 18 is coupled to a signal input ofcoherent detector 14. The output of coherent detector 14 is coupled to acapacity output tenninal 19.. The output of operational amplifier 18 isalso coupled through limiter 21 to a signal input of coherent detector16, the output of which is coupled through tangent function generator 22to a loss tangent dissipation factor output terminal 23.

OPERATION A typical use for the present invention is the monitoring ofsample polyester resin compression moldings for proper curing since theelectrical transfer characteristic of the resin, as a dielectric, willvary with its curing. Accordingly, a variablefrequency oscillator isutilized to optimize the metering of the sample since variations of thedielectric will vary the frequency transfer curve. l-Ience,variable-frequency oscillator is set at something near the optimumtransfer frequency of the sample and has a sine wave output which isintegrated in integrator 13. Integrator l3 shifts the sine wave signaland utilizes a transfer characteristic of l w. or one-half'lf. Hence,the reactive component of the sample 17, having a frequency which wouldtransfer the signal directly proportional to the frequency, will beoffset by the integrator 13 attenuating the signal inverselyproportional to the frequency rendering the entire dielectrometerinsensitive to frequency changes, i.e., automatically compensating forfrequency.

A quadrature square wave output is also taken from variable-frequencyoscillator 11 and applied to a reference input of coherent detector 16which also incorporates a low-pass filter. An inphase square wave signalis taken from the variablefrequency oscillator 11 and coupled to thereference input of coherent detector 14, which also incorporates alow-pass pass filter. It is pointed out here, that the waveformsappearing throughout the diagram correspond to voltage waveforms, hence,the sine-wave output from the vairable frequency oscillator 11 appearsas an 0 phase waveform and the output of integrator 13 a 90 shiftedwaveform. Since the output of sample 17 is converted to current by thelow input impedance of the operational amplifier 18, it does not appearas a voltage waveform. The output of operational amplifier 18 is thenthe result of a complex impedance represented by a capacitor andresistive network in sample 17 and is somewhere between 0 and 90 phasewith respect to the original 0 phase output of variable-frequencyoscillator 11. To measure this phase shift, this signal is limited inlimiter 21 and appears as a square wave at the input of coherentdetector 16. Since the reference from variable-frequency oscillator 11is in quadrature to the original sine-wave signal of variable-frequencyoscillator 11, it will be in phase with the output of integrator 13 andthe output of coherent detector 16 will appear as a voltage proportionalto the phase shift of the signal passing through sample 17. This signalis then passed through a tangent function generator 22, which yields asignal directly proportional to a loss tangent dissipation factor whichis expressed mathematically as D l w. RC, which is also equal to thetangent of 90 minus the phase shift of the signal passing through thesample.

A second signal is passed into the input of coherent detector 16 which,again, is the complex output of operational amplifier 18. This signal isreferenced with a square wave which is inphase with the sine-wave outputof variable frequency oscillator l1 and, hence, in quadrature with theinput to sample 17. The result is a signal and output terminal 21 whichhas an amplitude directly proportional to the capacitive component ofsample 17.

It should be understood, of course, that the foregoing disclosurerelates to only a preferred embodiment of the invention and that it isintended to cover all changes and modifications of the example of theinvention herein chosen for the purposes of the disclosure which do notconstitute departures from the spirit and scope of the invention.

We claim:

1. A dielectrometer for measuring electrical characteristics of adielectric sample comprising:

a signal generator having a sine-wave output and a square wave output 90removed in phase from said sine-wave output; i

a dielectric sample having an input coupled to said sinewave output;

limiting means, said limiting means having an input coupled to an outputfrom said dielectric sample;

a coherent detector, said square wave output coupled to a referenceinput of said coherent detector and a signal input of said coherentdetector coupled to an output of said limiter; and

tangent function generator means having an input coupled to an output ofsaid coherent detector whereby an output from said tangent functiongenerating means yields the dissipation factor of said dielectricsample.

2. The dielectrometer of claim 1 wherein:

said signal generator comprises a variable-frequency oscillator andfurther includes integrating means coupled between said sine-wave outputand said dieletric sample input.

3. The dielectrorneter of claim 2 and further including:

a second square wave output of said signal-generating means in phasewith said sine-wave output; anda second coherent detector having areference input coupled to said second square wave output and a signalinput coupled to an output of said dielectric sample whereby an outputfrom said second coherent detector yields the capacitive component ofsaid dielectric sample.

4. The dielectrometer of claim 1 and further including:

integrating means coupled between said sine-wave output and saiddielectric sample; and

an operational amplifier coupled between said dielectric sample outputand said limiting means.

5. A dielectrometer for measuring electrical characteristics of adielectric sample comprising:

a dielectric sample having an input and an output;

a signal-generating means having a signal output coupled to saiddielectric sample input;

a coherent detector having a signal input and a reference incouplingmeans coupling the output of said dielectric sample to said signalinput; and

said signal-generating means operable for generating a reference signalof the same frequency and predeterminedly related in phase to saidsignal output, said reference signal being coupled to said coherentdetector reference input whereby the output of the coherent detector isthe arctangent of the dissipation factor of the dielectric sample.

* i i i

1. A dielectrometer for measuring electrical characteristics of adielectric sample comprising: a signal generator having a sine-waveoutput and a square wave output 90* removed in phase from said sine-waveoutput; a dielectric sample having an input coupled to said sine-waveoutput; limiting means, said limiting means having an input coupled toan output from said dielectric sample; a coherent detector, said squarewave output coupled to a reference input of said coherent detector and asignal input of said coherent detector coupled to an output of saidlimiter; and tangent function generator means having an input coupled toan output of said coherent detector whereby an output from said tangentfunction generating means yields the dissipation factor of saiddielectric sample.
 2. The dielectrometer of claim 1 wherein: said signalgenerator comprises a variable-frequency oscillator and further includesintegrating means coupled between said sine-wave output and saiddieletric sample input.
 3. The dielectrometer of claim 2 and furtherincluding: a second square wave output of said signal-generating meansin phase with said sine-wave output; and a second coherent detectorhaving a reference input coupled to said second square wave output and asignal input coupled to an output of said dielectric sample whereby anoutput from said second coherent detector yields the capacitivecomponent of said dielectric sample.
 4. The dielectrometer of claim 1and further including: integrating means coupled between said sine-waveoutput and said dielectric sample; and an operational amplifier coupledbetween said dielectric sample output and said limiting means.
 5. Adielectrometer for measuring electrical characteristics of a dielectricsample comprising: a dielectric sample having an input and an output; asignal-generating means having a signal output coupled to saiddielectric sample input; a coherent detector having a signal input and areference input; coupling means coupling the output of said dielectricsample to said signal input; and said signal-generating means operablefor generating a reference signal of the same frequency andpredeterminedly related in phase to said signal output, said referencesignal being coupled to said coherent detector reference input wherebythe output of the coherent detector is the arctangent of the dissipationfactor of the dielectric sample.